Fix docker_container.container_logs to return demultiplexed log content

[Copilot]

docker_container.container_logs currently captures raw Docker log stream frames, so returned values include Docker multiplex headers (\u0001...) instead of actual container output. This breaks expected parity with docker logs output and can surface invalid/non-portable state payloads.

• Log stream handling

  • Switched container log collection in docker_container create/attach flow from line-scanning raw stream bytes to Docker-aware demultiplexing.
  • For non-TTY containers, logs are decoded with stdcopy.StdCopy so stream headers are removed.
  • For TTY containers, log bytes are copied as-is to preserve expected behavior.

• Error propagation

  • Replaced fatal/panic behavior in async log collection path with error propagation back to Terraform diagnostics, so failures are surfaced without terminating the provider process.

• Test updates

  • Updated acceptance expectation for container_logs to plain output (1\n2\n...) rather than header-prefixed frames.
  • Added focused unit tests for both demultiplexed and TTY paths.

func copyContainerLogs(dst io.Writer, reader io.Reader, tty bool) error {
	if tty {
		_, err := io.Copy(dst, reader)
		return err
	}

	_, err := stdcopy.StdCopy(dst, dst, reader)
	return err
}